It is proposed to study the homograft reaction by characterizing the interactions between sensitive lymphocytes and the sensitizing antigen under defined in vitro conditions. The inhibition of migration of sensitive cells by the specific antigen and the production of soluble mediators of cellular immunity by sensitive cells following incubation with antigen will be used as in vitro correlates for transplantation immunity. It is planned to study the influence of uremia on the expression of transplantation immunity by sensitive cells. Also, the in vitro responses of sensitive cells from immunologically suppressed recipients will be evaluated.